It is necessary to measure the concentration of gaseous and vaporous components of a fluid mixture comprising gases or gases and vapors or exclusively vapors for the various technical applications such s for monitoring workplaces which can include locations where washing is done with solvents such as in a chemical cleaning facility and operating rooms. However, this measurement can also be used for process control such as in chemical facilities and in the case of measuring breathing gas. The fluid mixture to be measured can comprise gases or gases and vapors or can be comprised exclusively of vapors. If required, the fluid mixture can also be monitored.
An arrangement for optically measuring material concentrations in fluid mixtures is disclosed in German published patent application DE-OS 3,344,019. In the arrangement disclosed in this publication, a measuring chamber made of a material which is transparent to the measuring radiation is provided for the optical measurement of material concentrations in the infrared range. The material is selectively permeable for the particles to be measured and interacts with the particles. This material defines a functional connection with the measuring object and the measurement radiation radiates therethrough. At the same time, it is provided that the particles to be measured accumulate in the membrane. The advantage of this arrangement is seen in that the selectivity and sensitivity of the measurement is increased by means of the accumulation of the particles to be measured in the membrane while being separated from other particles which are not to be measured and which can, however, be disturbing.